Non-halogenated and halogenated heterocyclic aromatic compounds in the Canadian environment

Abstract

Polycyclic aromatic compounds (PACs) are a broad class of pollutants with two or more fused aromatic rings, originating from petrogenic, pyrogenic, and biogenic sources. Hetero-polycyclic aromatic compounds (HPACs), a subclass of PACs that contains nitrogen, sulfur, and/or oxygen in their aromatic structure, are understudied despite growing evidence of their persistence, bioaccumulation, and toxicity. This is largely because the United States Environmental Protection Agency and Canada's Environmental Protection Act, 1999, recognize only 16 polycyclic aromatic hydrocarbons (PAHs) as priority pollutants, leaving other subclasses of PACs underrepresented in environmental monitoring. Consequently, my research was geared toward addressing the paucity of scientific data on HPACs. In doing so, I generated new knowledge on HPACs across several fronts. First, I developed and validated both targeted and non-targeted analytical methods for accurately measuring HPACs in environmental matrices. These methods were then applied to generate baseline concentration data for a broad suite of PACs, including 50 HPACs in Lake Erie biota, and Lake Ontario sediments, many of which had not previously been reported in these systems. Second, using advanced chemometric techniques, such as multivariate and cluster analysis, I demonstrated that HPACs have greater diagnostic power in deriving the sources, fate, and behaviour of PACs relative to their homocyclic counterparts. Notably, comparison of HPAC profiles in Lake Ontario sediments against coal-tar- and non-coal-tar-based reference materials revealed that Hamilton Harbour sediments are primarily contaminated by coal-tar-derived PAC sources, illustrating the real-world diagnostic value of HPACs. Third, I showed that HPAC distribution patterns clearly differentiated fish communities by habitat and physiological traits, such as biotransformation capacity and body size, whereas homocyclic PAC profiles were comparatively uniform, indicating weaker habitat-specific influences. Fourth, I developed a multi-tiered data-filtering framework to help the scientific community streamline the interpretation of high-resolution mass spectra to elucidate PACs in complex environmental matrices. Taken together, my research demonstrates the importance of this overlooked class of contaminants and highlights the need for the inclusion of HPACs into long-term monitoring and risk assessment frameworks, which will ultimately improve our understanding of the environmental behaviour and impacts of PACs across Canadian environmental systems.